How it works in one minute
App + MQTT
It was written in October 2026 from the integration's official documentation, but nobody in the Watt Budget community has followed it end to end on their car yet. Trying it? Tell me what works and what gets stuck.
(car's 4G)SAIC MQTT Gateway
(HA app)Mosquitto
(MQTT)Home
Assistant
| What it is | An app (add-on) that connects to the iSMART service like the MG app, then publishes the data to MQTT |
| Cost | Free |
| Data | Battery level, range, charging, power, time left, doors, windows, tyre pressure, 12 V battery, location |
| Commands | Climate, start and stop charging, charge limit, locking (not always reliable) |
| Where it works | Anywhere, through the car's connection |
| Depends on | MG's iSMART service and a secondary account |
What you need
- Home Assistant installed and reachable from your computer.
- The Mosquitto broker (official app, Settings → Apps → Store (Add-ons on older versions)) and the MQTT integration. If you already use Zigbee2MQTT, you have them.
- A car registered in the iSMART app (Europe), with connected services active.
- A second email address for the secondary account.
- A dedicated Home Assistant user for MQTT (for example
mqtt-mg, “local access only”, not an administrator).
1Install the integration
- Create the secondary iSMART accountIn the iSMART app, Profile page (last icon bottom right), add a secondary account with your second email address, with no expiry date, then confirm the email you receive. MG allows one login per account at a time: without a separate account, the app on your phone would keep getting logged out.
- Add the SAIC apps repositorySettings → Apps → Store (Add-ons on older versions) → ⋮ menu → Repositories, add
https://github.com/SAIC-iSmart-API/saic-home-assistant-addon, then refresh the page. - Install the gatewayPick SAIC MQTT Gateway from the list and install it.
- Fill in the configurationConfiguration tab: the email and password of the secondary account, region
eu(the default), then the MQTT user and password created above. Leave Home Assistant discovery enabled. - Start it and watch the logStart the app, tick “Start on boot” and “Watchdog”, then open the Log tab: the gateway should log in to iSMART and find the car's VIN.
- Find the carSettings → Devices & services → MQTT: a device named after the car appears, with its sensors and controls.
Its author no longer maintains it. If you use it, remove it before installing the gateway so the two don't fight over the login.
2The data you get
| Data | What it's for |
|---|---|
| Battery level (SoC) | In %, the value to give Watt Budget |
| Electric range | Kilometres estimated by the car |
| Charging / cable plugged in | To trigger an automation when you arrive or when charging ends |
| Power and charge time left | While charging |
| Charge limit (target SoC) | Adjustable from Home Assistant |
| Doors, windows, boot | Handy for an evening “window open” alert |
| Tyre pressure | All four wheels |
| 12 V battery | Useful to spot a car that no longer goes to sleep |
Replace the long names with short ones, for example sensor.mg_battery (Settings → Devices & services → Entities → the entity → cog). Your cards, automations and Watt Budget settings will be much easier to read.
3Connect Watt Budget
The sensor to enter in Watt Budget, under Settings › Home Assistant: the SoC sensor (battery level in %) of the car's MQTT device.
Once connected, Watt Budget reads the level every minute: no more typing the starting percentage, and the charge is worked out from the real battery level.
The four steps (HTTPS access, token, sensors, check) are explained on the guides home page and in the Watt Budget guide.
4Precautions
- When you open the iSMART app with the main account, the gateway pauses for 15 minutes by default: that's normal.
- The lock command sometimes fails (the car thinks a key is still inside): don't rely on it for security.
- Non-plug-in hybrids (MG3 Hybrid+) report little data.
- Unofficial integration: the manufacturer can change its app and break it overnight. Keep the official app on your phone.
- Don't shorten the update interval: each query can wake the car and drain its 12 V battery. The defaults are a good balance.
- Your credentials stay in your Home Assistant; neither Watt Budget nor I can see them.
Frequently asked questions
Why a secondary account?
MG's servers allow one session per account. With a single account, the gateway and your phone app would keep logging each other out.
The gateway can't connect any more. What now?
Check that the secondary account hasn't expired in iSMART. Several owners fixed it by deleting and recreating the secondary account.
Does Watt Budget get access to my car?
No. Watt Budget only reads the battery level sensor in your Home Assistant, from your browser, with the token you give it. It never sees your manufacturer login or the car's location.
My model isn't listed. Can it work?
Often yes: these integrations go through the manufacturer's app, shared across the range. The easiest is to try, then tell me how it went via the contact page.
Links and thanks
- github.com/SAIC-iSmart-API/saic-home-assistant-addon
- github.com/SAIC-iSmart-API/saic-python-mqtt-gateway
Thanks to the developers of the SAIC-iSmart-API project, who maintain the gateway, and to the MG owners' community documenting the car's data.
Does your car reach Home Assistant another way? Share your method: the next guides will follow your feedback.
The other Home Assistant guides
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